Spark ignition systems



1968 B. PHILLIPS ETAL 3,406,672

SPARK IGNITION SYSTEMS Filed March 8, 1966 L M 1 Q1! wm i \w 4 cw Q 3 WNN M ma k Q \w Mm United States PatentO 3,406,672 SPARK IGNITION SYSTEMS Brian Leslie Phillips, Handsworth, and Derek Stanley Adams, Acocks Green, England, assignors to Joseph Lucas (Industries) Limited, Birmingham, England, a British corn an File d Nlar. 8, 1966, Ser. No. 532,712 Claims priority, application Great Britain, Mar. 10, 1965,

10,110/ 65 2 Claims. (Cl. 123-148)' ABSTRACT OF THE DISCLOSURE In a spark ignition system, for an internal combustion engine, an inductor is connected in series with a switch across a battery. The switch is closed at periodic intervals by the engine through the intermediary of a transformer, and when it closes energy is stored in the inductor, this energy later being used to produce a spark ata plug of the engine in timed relationship thereto. When the current flowing in the inductor reaches a predetermined value, a circuit is rendered operative to turn the switch off through the intermediary of a second transformer, so that the energy stored in the inductor each time the switch closes is constant.

. This invention relates to spark ignition systems for internalcombustion engines.

In its preferred form, the invention makes use of a semi-conductor device known as a gate controlled switch. This device is similar to the semi-conductordevice called a controlledrectifier, but has theadditional property that it can be switched off by a negative current flowing between its gate and cathode, whereas a conventional controlled rectifier can only be switched off by a reverse voltage between its anode and cathode. The gate controlled switch can handle currents of the same magnitude as the controlled rectifier, and should not, be confused with devices such as the trigistor' which operates in a similar manner, but can handle only very small anode-cathode currents. The gate controlled switch is one example of a. semi-conductor switch, which term is hereby defined to means a semi-conductor device having a control terminal, and a pair of main terminals, signals applied to the control terminal determining whether or not the switch conducts. In the case of a gate controlled switch, the main terminals are the anode and cathode and the control terminal is the gate. If a transistor is used, the collector and emitter constitute the main terminals and the base the control terminal. It will be noted that the definition excludes, for example, a controlled rectifier, even though a controlled rectifier has the necessary three terminals, because although the gate signal applied to a controlled rectifier initiates conduction, turning off of the controlled rectifier can only be effected by reversing its anode-cathode voltage.

A spark ignition system according to the invention includes a semi-conductor switch controlling the production of the required sparks, and a pair of transformers providing signals to the control terminal of said switch for turning the switch on and off respectively.

The accompanying drawing is a circuit diagram illustrating one example of the invention.

Referring to the drawing, there are provided positive and negative lines 11, 12 connected in use to a vehicle battery. Connected in series across these lines are an inductor 13, a diode 14, a gate controlled switch 15 and a resistor 16. The switch 15 is a semi-conductor device having the properties of a controlled rectifier with the addi- "ice tional property that anode-cathode current can be switched off by a negative gate-cathode current.

Connected between the gate and cathode of the switch 15 in series with a diode .17 and Zener diode 18 is the secondary winding 19 of a transformer 21 the primary winding 22 of which has one end connected to the line 11 and its other end connected to the collector of a transistor 23, the emitter of which is connected to the line 12, and the base of which is connected to the collector of a transistor 24. The transistor 24 has its emitter connected to the line 12, its collector connected to the line 11 through a resistor 25 and its base connected to a terminal 26, through a resistor 27 to the line 11, through a resistor 28 to the collector of the transistor 23, and through a resistor 29 and the resistor in series to the line 12.

The gate and cathode of the switch .15 arefurther interconnected through the secondary winding 31 of a transformer 32 having its primary winding connected between the line 11 and the collector of a transistor 34 having its emitter connected to the line 12 through a resistor 35 and its base connected to the collector of a transistor 36. The transistor 36 has its emitter connected to the line 12, its collector connected through a resistor 37 to the line 11, and its base connected to the line 12 through a resistor 38 and the resistor 35 in series, and to the line 11 and the collector of the transistor 23 through resistors 39 and 41, respectively.

The anode and cathode of the switch 15 are interconnected through a capacitor 42 in series with the primary winding 43 of an ignition transformer 44, the secondary winding 45 of which is connected through a distributor 46 to the plugs 47 of the engine in turn. The winding 43 is bridged by a diode 48.

In order to understand the operation of the circuit, consider a point in a cycle at which the switch 15 is off and the capacitor 42 is charged. In this condition the transistors 24 and 36 are on, but the transistors 23, and 34 are off. Thus, no current flows in the winding 22 or the winding 33.

At the instant when a spark is required, any convenient known means operated by the engine causes a negative signal to appear at the terminal 26. This signal turns the transistor 24 off, and so the transistor 23 is turned on, and current builds up in the winding 22. The rising current produces an in the winding 19, but this is blocked by the diode 17. When the transistor 23 is switched on, the transistor 36 tends to switch oif and the transistor 34 tends to switch on. The transistors 34, 36 act in conjunction with their associated components to cause a pulse to be applied to the winding 33 until the transistor 23 is turned off in a manner to be described. By virtue of the connections of the circuit, this pulse will have an amplitude independent of the battery voltage, and so a substantially constant current is fed by the winding 31 to the switch 15 to turn it on. The Zener diode 18 prevents the turn-on current from flowing through the winding 19.

When the switch 15 is turned on, the capacitor 42 discharges through the winding 43 to produce the required spark. While the switch 15 is on, current builds up in the series circuit 13, 14, 15, 16 until, when a predetermined current is reached, the voltage across the resistor .16 turns the transistor 24 on. The transistors 34, 36 now revert to their original state, so removing the forward drive to the switch 15, and the transistor 23 is turned ofi to break the current in the winding 22. The resultant E.M.F. in the winding 19 provides a negative gatecathode current to turn the switch off. The energy stored in the inductor 13 is now transferred to the capacitor 42 by way of the diode 48 and retained by the diode 14, and it will be appreciated that the capacitor 42 will be charged to a volta g e considerably in excess of battery voltage. The c 'ci"isre eatemwhena further signal is received at the terminal 26.;

The resistors 27, 29 provide compensation for changes in battery voltage, and the windings 13, 22 are chosen to have a high inductance-resistance ratio. Inthiswa'y', the current flowing through the winding 13 when the switch 15 is turned oif is rendered substantially independent of battery voltage. The Zener diode 18 dissipates energy remaining in the winding 19 after the'switch 15 is turned off V In a modification particularly useful where the battery voltage may bdextreme'ly'low', the resistors 25,27 are connected to the line 11' through an additional resistor, and a point intermediate the additionalresistor and the resistors 25, 2 7 'is connected to the line .12 through a Zener diode. v

As previously explained, a transistor can be used in place of a gate controlled switch, it then being necessary to ensure that the transistor remains saturated whileit is on. This can be done by ensuring that sufficient base 'current is provided to saturate the transistor at any expected collector emitter current, or by incorporating a transformer to increase the base drive with increasing collector-emitter current. In the drawing current is provided to turn off the gate controlled switch, and it will be understood that where a transistor is used the removal of the drive current is sufiicient to stop the transistor conducting.

However, the use of the circuit shown is advantageous even with a transistor, because the reverse base-emitter bias ensures that the transistor switches ofi rapidly.

It will be appreciated that the idea of using two transformers to provide turn-on and turn-01f pulses can be used in numerous other ignition systems, and has the advantage that more accurate control can be obtained than if a single transformer'is used for both purposes.

Having thus described our invention what we claim as new and desire to secure by Letters Patent is:

1. In an ignition system for an internal combustion engine, which system has an ignition coil for supplying high voltage firing pulses to the internal combustion engine and pulse means in synchronism with the internal combustion engine and having an electrical source; a firing circuit for providing intermittent current flow in the ignition coil to produce firing pulses therein, including in combination, a capacitor; a gate controlled semiconductor switch connected in series with said capacitor and the ignition coil; said semiconductor switch having a gate region responsive to a pulse of a given polarity to turn on said semiconductor switch and responsive to a pulse ofopposite polarity to turn off saidsemiconductor switchj an 11136615566 aiida diode connecte d in series with said semiconductor switch and said capacitor in parallel so that current flows through said inductance and diode and the semiconductor switch when said switch is on and flows into said capacitor when said switch is said d od f t dnact 1' s si r s t .19? frpni said capacitor through said inductance byjd' ch rg'e of said capacitor'therethrough;.a.resistor; means 5; necting said series connected inductance, dio de,t,and:, semi conductorswite'h in a seriescircuitawithsaid resistor; means connecting-said series circuit across said electrical source whereby current flows"theret hrough when said semiconductor switchis on; ine'ans' cdupled to the pulse means to apply pulses of the-given polarity to said gate region to; turn on sgu'd semiconductor switch and discharge said capacitor through said ig'n'ition c o'il for producing a firing pulse thereinya transformer havingaprimar'y' winding and-"a secondary winding; meansforaconnecting and disconnecting 'said primary winding to the electrical source; unidirectionalcurrent means connecting said secondary winding to said switch "gate region Lfor response to current-flow 'in said primary winding on. deenergization of said primary winding for applying a pulse to said gate-region to turn otf said semiconductor switchyand means responsive to the voltage across said resistor for disconnecting said primary-winding from said electrical source whereby saidsemiconductor switch.:is turned off causing said inductance to discharge into said capacitor and charge the same i 2. An ignition system as defined in claim 1 wherein said means'coupled 'to the pulse means comprises a sec- 7 0nd transformer having a primary'windin'g-and-"a second- References Cited UNITED STATES PATENTS 2,347,489 8 1958 Shortetal. 3,150,286 9/1964 Quinn. 3,271,593 9/1966 De Vilbiss. 3,306,275 2/1967 Hutton.- 3,318,296 5/1967 Hufton.

LAURENCE M. GO'ODRIDGE Prim'ary Examiner. 

